Schottky diodes are commonly used in applications requiring fast switching, for example, in power circuits. Also, while standard silicon diodes have a forward voltage drop of about 0.6 volts, Schottky diodes' voltage drop at forward biases of around 1 mA is in the range of 0.15 V to 0.45 V, making them useful in voltage clamping applications and in applications for preventing transistor saturation. This is due to the Schottky diode's higher current density.
FIG. 1 illustrates a cross-sectional view of a conventional Schottky diode 100, which includes metal-containing layer 104 formed on an n-type well region 102. Shallow trench isolation regions 106 surround metal-containing layer 104. Metal-containing layer 104 and n-type well region 102 form a Schottky diode, with metal-containing layer 104 acting as an anode, and n-type well region 102 acting as a cathode.
Schottky diode 100 suffers from a low breakdown voltage. FIG. 2 illustrates an I-V curve of Schottky diode 100, wherein the X-axis indicates the reverse voltage VR applied on Schottky diode 100, and the Y-axis indicates the leakage current IR. It is noted that with the increase in the reverse voltage VR, the leakage current IR keeps on increasing. Further, breakdown starts to occur at a reverse voltage of about 20 volts.
FIG. 3 illustrates a cross-sectional view of a modified Schottky diode 200. In addition to the components illustrated in FIG. 1, Schottky diode 200 further includes a p-type ring 122 around edges of metal-containing layer 104. The leakage current of Schottky diode 200 is thus improved over Schottky diode 100. FIG. 4 illustrates an I-V curve of Schottky diode 200, wherein the X-axis again indicates the reverse voltage VR applied on Schottky diode 200, and the Y-axis indicates the leakage current IR. It is noted that the leakage current of Schottky diode 200 is significantly reduced than the leakage current of Schottky diode 100 (refer to FIG. 2). However, the breakdown voltage is still only about 30 volts or less, which is far lower than the ideal breakdown voltage of about 60 voltages. Accordingly, what is needed in the art is a Schottky diode with a low leakage current and a high breakdown voltage.